1. Field of the Invention
The present invention relates to a process for producing naphtha and gas oil by a catalytic cracking of a plastics-derived liquid, which is obtained from a pyrolysis process, using a very low cost catalyst under low temperature and pressure conditions.
2. Description of the Related Art
The total amount of plastic waste is increasing every year. However, most plastics cannot rapidly degrade in a landfill and thus, become a major waste in garbage. Moreover, it is not environmentally friendly to dispose plastic waste by incineration, which leads to carbon dioxide and other greenhouse gas emissions even though incineration can generate energy. Moreover, incineration of plastics still has some drawbacks, such as high capital and maintenance cost. An alternative process to decompose plastic waste to generate energy and useful gaseous products is gasification. However, a conventional gasification process releases tars, heavy metals, halogens and alkaline compounds etc., and causes environmental problems. Another effort to utilize plastic waste, which seems to be promising, is the pyrolysis of plastic waste, resulting in a mixture of hydrocarbons of heavy oils and olefins.
Some of the present inventors previously proposed an environmentally acceptable process for disposing of scrap plastic material that contains inorganic matter in admixture with a comminuted aluminosilicate containing material to produce a synthesis gas, reducing gas, or fuel oil (U.S. Pat. No. 5,656,042). US Patent Publication No. 2007/0173673 discloses a method for catalytically cracking plastic waste and an apparatus for catalytically cracking plastic waste by using a granular FCC catalyst. International Application No. PCT/IN2004/000366 discloses a process for preparing a catalyst containing faujasite zeolite, pseudoboehmite alumina, polyammonium silicate, kaolin clay for catalytic cracking of plastic waste. Furthermore, US Patent Publication No. 2003/0019789 proposes development of a method of converting plastic waste material into gasoline, kerosene and diesel oil fraction. EP 0 535 253 describes a process for producing fuel oil and gas by cracking rubber and plastic waste at a low temperature of about 280° C. EP 0 535 253 discloses gas products which are further filtered, condensed and fractioned into light oil, heavy oil and gas. Moreover, it discloses a catalyst that is composed of 20% by wt. of CaO, 50% by wt. of Ni, 30% by wt. of XT-10, where XT-10 is a mixture of one or more of dolomite, garbbro, microcline, muscovite, tourmaline, talc, limestone etc. or China clay.
A similar process using laterite in the presence of dolomite ore is disclosed in U.S. Pat. No. 4,224,140, where catalytic cracking of a heavy oil by using laterite or a laterite-containing catalyst produces cracked distillate and a hydrogen-rich gas. U.S. Pat. No. 4,298,460 discloses a process for processing sulfur containing a heavy oil, which includes catalytically cracking the sulfur-containing heavy oil to produce a cracked distillate and hydrogen. U.S. Pat. No. 4,325,812 discloses a process for cracking heavy hydrocarbon into light oils and producing hydrogen by using a catalyst containing at least 30 wt. % of Fe in the presence of dolomite ore. However, none of these methods is efficient and is associated with high cost. And, prior to the present invention, none of the methods used dolomite itself as catalytic cracking catalyst for cracking heavy oil from plastic waste into light and heavy naphtha.
The present inventors discovered that dolomite by itself is capable of acting as the main catalyst if it is calcined at temperatures over 900° C. before it is used in the reaction.